When soft handover is employed in a line switching system, scheduling is not carried out since dedicated channels are at any time established with plural cells (sectors).
In a 4th Generation (4G) mobile system, all the communications are carried out through packets. In such packet communications, a shared channel is provided and time divisional control is employed in such a manner, for example, that the channel is allocated to a user 1 for a moment and to a user 2 for the next moment. Therefore, when soft handover is carried out between sectors, the transmissions to a user cannot be carried out unless the allocations are simultaneously carried out in both sectors.
Therefore, an algorithm for fast packet scheduling in soft handover over plural sectors is required.
The scheduling algorithm when handover is carried out includes, for example, an algorithm that enables scheduling only in one connected cell (sector) as the algorithm for scheduling when hard handover is carried out. While connection with either one of the users is established at a certain moment, the user moves to the next sector at a certain moment. Here, connection is made only to one cell (sector) at a certain moment, which means one link is kept. In this case, the cell (sector) in which scheduling is carried out is changed by such a handover. Namely, control over plural cells (sectors) is not required and control which is the same as the scheduling that does not take account of handover is carried out.
In addition, as the scheduling when soft handover is carried out, there is an algorithm that enables scheduling that takes account of a traffic class in an upper station (see non-patent documents 1, 2). For example, when there are two base stations and an upper station that controls these two base stations, it is the upper station that carries out the scheduling.
In addition, when soft handover is carried out in W-CDMA, plural sectors transmit simultaneously using different scramble codes for identifying sectors. A mobile station performs despreading on the signals transmitted from the sectors using scramble codes corresponding to the sectors and synthesizes the despread signals.
When different data are transmitted from two sectors using identical scramble codes, the mobile station receives the two transmission signals. However, the two signals are mixed and the two pieces of data transmitted from the two sectors cannot be identified.
Non-patent document 1: D. Zhao, “Effect of Soft Handoff on Packet Transmissions in Cellular CDMA Downkinks,” IEEE ISPAN '04, pp. 42-47, May 2004.
Non-patent document 2: M. Kazmi, et. al., “Scheduling Algorithms for Soft Handoff in Cellular Packet CDMA,” IEEE PIMRC 2000, pp. 671-675, September 2000.
Non-patent document 3: 3GPP TR 25.848 V4.0.0(2001-03)
Non-patent document 4: A. Jalali, R. Padovani, R. Pankaj, “Data Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal Communication Wireless System,” IEEE VTC 2000, pp. 1854-1858, 2000